Ben Bernanke is leaving the building. What a performance it's been. Though the Federal Reserve chairman's term will not end until Jan. 31, he's already made enormous moves to cement his legacy. On Dec. 18, Bernanke announced that the Federal Reserve would initiate the much feared "taper."

The taper, which has been expected for months, refers to the winding down of the Federal Reserve's quantitive easing program, or QE. QE was a massive asset-buying program on behalf of the Fed, one of Bernanke's landmark projects to ease the pain of the 2007- 2008 financial crisis.

Investors had been nervous for months about the Federal Reserve pulling back from its bond-buying program, fearing that if Bernanke acted too soon, there would be a strong market reaction and negative effects on economic growth. Bernanke could have initiated the so-called taper in September, but by waiting until December he gave investors time to prepare. It worked: Stocks soared after his announcement.

Bernanke didn't start this job with such instincts for timing. His first steps in office were small interest rate increases that look, in retrospect, to have been far too timid. He hadn't been in office long when the financial crisis hit. But when it did, Bernanke, a scholar of the Great Depression, took immediate and drastic action. His policies - which included bailing out financial institutions, maintaining extremely low interest rates, and the unconventional bond-buying stimulus program known as QE - have been controversial. They have also been effective. Thanks to Bernanke, the U.S. has done much better than other advanced nations after the crisis. The European unemployment rate is 12.1 percent, compared with 7 percent in the United States. The difference has been aggressive monetary policy.

That's not to say that Bernanke has been perfect. Critics will grumble that he shouldn't have started tapering while inflation remains below the Fed's annual 2 percent target rate and unemployment is still high. Others will note that his vigorous intrusion into the markets may have led to asset bubbles. They may be right. U.S. stock prices were up 26 percent in the last year, a number that should make any wise investor wary. And it's difficult to call Bernanke's tenure totally successful when economic growth is still sluggish and so many Americans have lost wealth or their jobs.

But, most of those problems can't be blamed on Bernanke. A highly partisan Congress that refused to use an expansionary fiscal policy, structural economic changes, and damage to the financial system after the crisis all had at least as much to do with the country's sputtering growth. Central banking is a powerful tool, but it works best when the rest of the government is working, too.

During a discussion with high school teachers last month, Bernanke said, "I wish I was leaving with the unemployment rate at 5 percent instead of 7 percent." Unemployment, and how to use central banking to combat it, will be one of the biggest issues that his successor, Fed Vice Chair Janet Yellen, faces. Yellen has made it clear that unemployment will be one of her top priorities, especially in the face of stubbornly low growth and inflation. But Bernanke's tenure proves that it won't be easy for Yellen or anyone else to fight unemployment with the Reserve's limited tools. Yellen will also face restive Fed governors in different parts of the country, many of whom want the Fed to return to a pre-crisis level of activity.

In short, Bernanke is handing Yellen the Fed at the beginning of a new, difficult, market cycle. But it's still a lot easier than the one that he inherited. With a reputation for consensus and an impressive body of knowledge all her own, Yellen should be able to handle the ups and downs. She, as with the rest of the country, should be grateful that Bernanke's good timing extended to understanding when it was time to leave.